This study investigates the long-term effectiveness of active psychological inoculation as a means to build resistance against misinformation. Using 3 longitudinal experiments (2 preregistered), we tested the effectiveness of Bad News, a real-world intervention in which participants develop resistance against misinformation through exposure to weakened doses of misinformation techniques. In 3 experiments (NExp1 = 151, NExp2 = 194, NExp3 = 170), participants played either Bad News (inoculation group) or Tetris (gamified control group) and rated the reliability of news headlines that either used a misinformation technique or not. We found that participants rate fake news as significantly less reliable after the intervention. In Experiment 1, we assessed participants at regular intervals to explore the longevity of this effect and found that the inoculation effect remains stable for at least 3 months. In Experiment 2, we sought to replicate these findings without regular testing and found significant decay over a 2-month time period so that the long-term inoculation effect was no longer significant. In Experiment 3, we replicated the inoculation effect and investigated whether long-term effects could be due to item-response memorization or the fake-to-real ratio of items presented, but found that this is not the case. We discuss implications for inoculation theory and psychological research on misinformation. (PsycInfo Database Record (c) 2021 APA, all rights reserved).